Heavy metal toxicity and trace metal deficiency have been implicated as factors in several psycho-pathological conditions. In an effort to further the understanding of the role of trace metals in behavior and brain function, the present work focuses on the issue of zinc in the hippocampus. The first goal is to develop for use with brain tissue a microanalytic zinc assay method based on stable isotope dilution mass spectrometry. Immediate applications of the method will include determining the regional distribution of zinc within the hippocampus and determining the zinc content of particular types of hippocampal cells; subsequent applications will include tests of the roles of trace metal disturbances in emotional and cognitive disorders.